ごめんなさい

ごめんなさい is a sincere apology used when admitting fault or wrongdoing.

FORMS:

• ごめんなさい: standard polite
• ごめん: casual
• ごめんね: casual, softer

COMPARISON WITH OTHER APOLOGIES:

• ごめんなさい: heartfelt, admits fault, personal situations
• すみません: lighter, also means "excuse me," broader use
• 申(もう)し訳(わけ)ありません: very formal, business/serious situations

USAGES:
1. Apologizing: ごめんなさい、私(わたし)が悪(わる)かった (Sorry, it was my fault)
2. Declining: ごめんなさい、今日(きょう)は無理(むり)です (Sorry, I can't today)

NOTE:
ごめんなさい sounds childish in formal business contexts; use 申(もう)し訳(わけ)ございません instead.